The present invention relates to a device for adjusting a rotational angle relationship between a camshaft and its drive element.
More particularly, it relates to a device of the above mentioned general type in which the drive element has two circular segment shells movable relative to one another in a setting direction and connected so that during adjustment in the setting direction the shells are adjusted in opposite directions and the volume enclosed in a working space between the shells increases when the volume in the other working space decreases.
A device for adjusting the rotational angle relationship of a camshaft is known from EP-A-0,163,046 in which two hydraulic servomotors located on a diameter of a part connected to the camshaft are provided, each servomotor having a servo-piston, each of which acts via a roller on a ramp which is located on a drive gearwheel radially enclosing the part connected to the camshaft. The ramps respectively associated with the servomotors are inclined in opposite directions in such a way that when the servo-piston of one servomotor is adjusted, the camshaft is adjusted by means of the ramp relative to the drive gearwheel in such a way that the opposite ramp pushes the servo-piston of the other servomotor back. The servomotors are triggered by valves or a spool valve in such a way that the outwardly moving piston of one servomotor is subjected to pressure and the working space of the other, opposite servomotor is relieved so that the piston of the servomotor can move away following the ramp. In such a device, a separate pressure source and magnetic valves for controlling the servomotors are necessary.
German Application P 39,30,157, which is not a prior publication, describes a device for adjusting the rotational angle relationship of a camshaft used, in particular, to actuate gas exchange valves of an internal combustion engine, which device has two servomotors acting oppositely to one another whose movable walls corresponding to one another are connected together. In order to reduce the requirements for the provision of the setting medium and the generation of pressure in this setting medium, the working spaces of the servomotors are both connected via one non-return valve each to a setting medium pressure source, on the one hand, and, on the other, can be selectively and directly connected or separated from one another by means of a control valve so that torque fluctuations in one of the working spaces and the resulting pressure can be specifically used at certain times for adjustment, the working spaces being subsequently shut off again.
The mode of operation of the camshaft adjustment device described in Patent Application P 39,30,157, which is not a prior publication, is therefore based on the fact that positive and negative torque fluctuations, relative to the average drive torque, appear alternately over the whole of the rotational speed range. The working spaces of the servomotors are acted on by a spring in such a way that the spring acts in the sense of increasing the working space of a servomotor. Because the preload on the spiral spring is selected to correspond precisely to the average drive torque, a positive pressure similarly appears alternately in the working spaces. By means of a control valve, these pressure peaks can be used directly and specifically as the pressure medium source for adjustment.
Operation, however, is problematic at low engine rotational speeds and at the starting rotational speed of the engine because the torque fluctuations become smaller, at an average drive torque, because of decreasing mass forces. If deviations now occur in the average torque due to temperature changes or variations between individual units, it may happen that the camshaft can only be adjusted in one direction.